Human contribution to per-capita wealth should be approximately zero post-AGI, so I don't fully agree with the last part. But I still agree that repugnant conclusion arguments smuggle in a resource assumption.
It has always bothered me that people assume that the “repugnant conclusion,” perhaps because of the name, must actually be the conclusion of total utilitarianism. But it just isn't—it's only the conclusion of total utilitarianism in crazy hypotheticals that assume that making people happier is extremely resource intense relative to supporting new people.
If someone asks me to consider what happens if a fair coin has flipped 1,000 times heads i na. row, i'm going to fight the hypothetical; it violates my priors so strongly that there's no real world situation where i can accept the hypothetical as given.
I think what's being smuggled in is something like an orthogonality thesis, which says something like 'worldstates, and how people feel, are orthogonal to each other.'
Why malthusian arguments is a failure state is still a little high on the abstract layers. I believe it is because then killing off an outgroup becomes a valid or percieved as an unavoidable solution model.
I could not really follow why declining population causes a crisis of meaning.
But consider what happens next: the population of the island will stabilize, and then over years and generations, they will get better at making food and material wealth.
Hmm. How sure are you of that? It seems more likely that the population will fall too far, then grow too far, in a cycle that may or may not support average improvements in food and wealth that make each cycle somewhat larger (or maybe, but not guaranteed, tamps down the amplitude to closer to a smooth increase).
we will soon live in a world of nine or ten billion people, very few or none of them in deep poverty
I'm halfway-agreed. There will probably be no major population decrease, but I suspect and fear that the disparity between rich and poor (fractally and relatively, both within industrialized regions and compared across continents and nations) is going to get much greater. There will be many in "deep" poverty, even though the depth is arguable (mostly argued among elites and the rich), who will not get the benefit of the incredible art, Mars exploration, or abundant energy that the minority (still billions, but nowhere near universal) of humans enjoy.
I don't have an opinion on whether this is a better outcome than half as many people, with somewhat less of a top achievement (maybe not on Mars yet) much less disparity in wealth and satisfaction. But that's the question of the Repugnant conclusion. It's easy to reformulate as "worst lives" instead of "average lives". Which is still Malthusian in nature. I'd argue it's not "smuggled in", but central to the question of what's a better population size.
You definitely have a good and important point. I think in the short term (a few centuries out), you're right that more people will not just increase total welfare but also increase average welfare (... at least under some reasonable conditions).
However, long term it seems like one would expect to eventually hit Malthus-like issues. There's presumably diminishing returns to everything, including labor and ingenuity.
Scott Alexander and others in this part of the internet have been debating the Repugnant Conclusion recently. (I'll assume you're up-to-date on this discussion. If you aren't, follow the link, or just google "Repugnant Conclusion" or "Mere Addition Paradox".)
Many have noticed that there is a problem with the argument: the world-state that is described as 'repugnant' actually isn't so bad. Trillions of people just chilling -- living out their lives -- and not, on balance, suffering, is a much better world than the one we currently inhabit, where the rabbit runs for his life and the fox runs for his dinner. So if you force me to accept the hypothetical, then my answer is yes, World Z please.
But my beef with the Repugnant Conclusion goes beyond the abstracted hypothetical. This discourse maps perfectly to a real world debate we are actually having in the real world of 2022. It's a question about hard policy issues, abstracted just enough to get past knee-jerk partisan reactions. It seems like few have noticed this connection, although I suspect that people do notice it but would prefer to elide it, since this ultimately does get into politics. The actual policy question is as follows: Is the world, today in 2022, overpopulated? And, was Malthus right?
The Repugnant Conclusion asks you to consider a number of possible world-states in which there are some number of living people, each with some amount of average happiness. The set of possible world-states offered is arranged such that the more populous worlds contain less average happiness. But why would you think that adding more people reduces the average happiness?
Imagine that the entire universe consisted of just one person, Sally, living on a small island. She can eat the nuts and berries from trees, and has a source of water, etc, so she is not suffering in the material sense. Call this World A. Now let's give her a friend, Kim, to keep her company. There are now two people, and still plenty of nuts and berries to go around. Call this World B. Hopefully you will agree that World B is much better than World A, not just in terms of total happiness, but in terms of average happiness. Sally now has a friend. But also, Kim and Sally working together can produce more material wealth than either can alone. Perhaps Kim is better at building shelters, and Sally is better at foraging. (Standard economics, blah blah)
Now, World Z: Let's cram the entire population of Akron, Ohio (two hundred thousand people) onto this tiny island. Clearly, the island cannot provide a comfortable lifestyle for so many people. The carrying capacity of the island is somewhere between 2 and 200k. World Z contains an immense amount of suffering, and also death. Assuming that they don't drive all sources of food to extinction, the population of World Z will eventually fall to the carrying capacity of the island. Clearly this is a disaster. But consider what happens next: the population of the island will stabilize, and then over years and generations, they will get better at making food and material wealth. They will develop their skills, build infrastructure and maybe even invent technology. Eventually they will build a raft and find new land. Civilization will happen.
Do you want civilization? Many people in the world today are deeply concerned that industrial civilization is heading for disaster. They believe that we must radically reduce our population -- Island Earth cannot sustain eight billion people -- and that our material consumption must be severely restricted. The alternative, business-as-usual, will result in a massive amount of human suffering, die-offs due to famine etc, and the total destruction of nature. In this view, we already live in World Z.
I don't share this view, and I think most people in this community don't share this view. There seems to be an emerging consensus among us that climate change, while real and serious, is not end-of-civilization-billions-dying serious. Given continued economic growth and a transition to new energy sources, we'll be okay. In fact, we'll be better than okay! My prediction is that (ignoring AI/the singularity for the moment) we will soon live in a world of nine or ten billion people, very few or none of them in deep poverty, with abundant carbon-free energy, humans landing on Mars, beautiful art and other wonders beyond our imagination.
My view is based on the book Merchants of Despair by Robert Zubrin. To be honest, this book is tedious and partisan; it's not Zubrin's best work. (I would recommend The Case for Mars instead.) But Zubrin does put forth an very important argument in Merchants of Despair: that each additional person increases the material wealth of civilization on a per-capita basis. Far from the Repugnant Conclusion, adding people makes everyone better off. There are plenty of atoms and more than enough land. What is limited is the labor and ingenuity to turn matter into resources. The world is not overpopulated, and will never be overpopulated. In fact, if birthrates continue as they have been, the population will decline. According to Zubrin's model, our per-capita wealth will then decline as well. I also believe that a childless, declining population causes social problems and a crisis of meaning. This is much worse than a decline in per-capita income, but hard to capture in numbers.
My beef with the Repugnant Conclusion is that it smuggles in a Malthusian argument. I'm not going to accuse anyone of arguing in bad faith; the reason why we keep talking about population ethics in abstract analytical terms is because we are people who like to play with abstract analytical puzzles, and no one in this community (that I've seen) is a hard-core partisan exclaiming eminent doom from industrial-environmental catastrophe. (We do talk about another kind of doom, but not environmental.) Nevertheless, if you demand that that I not fight the hypothetical, you are asking me to accept a worldview that I see as false. I guess I don't actually like to play with abstract analytical puzzles; I'd rather focus on the ground truth.